1. Field of the Invention
The invention relates to a temperature controlled exhaust assembly for a semiconductor wafer processing system and, more particularly, to an integrated exhaust assembly having temperature control with cold trap capability.
2. Description of the Background Art
In the development of wafer processing equipment for device manufacture, the design of an exhaust system may be as important as that for the process chamber. Many, if not most, of the processes used in semiconductor device fabrication involve either corrosive or toxic chemical precursors. Very often, the process reactions lead to similarly toxic by-products, or leave undesirable deposits on interior surfaces of the chamber and/or exhaust assembly. Therefore, the design of an exhaust system should address environmental concerns and safety considerations for operating personnel, as well as the need for ease of maintenance of system components.
Different types of traps are commercially available for use in an exhaust line to trap a variety of chemicals. Examples include molecular sieve traps which work by chemisorption and cold temperature traps for trapping condensable materials. Off-the-shelf cold traps typically involve only a single stage design, and may not have sufficient trapping efficiency to meet certain processing demands. One example of a process that exceeds the capabilities of existing cold traps is the deposition of titanium nitride (TiN) film from a reaction between titanium tetrachloride (TiCl.sub.4) and ammonia (NH.sub.3). In addition to the reaction products titanium nitride (TiN), nitrogen (N.sub.2) and hydrogen chloride (HCl), other by-products such as adduct ammonia salts are formed. It is found that existing single-stage cold traps cannot effectively trap reaction by-products under certain operating and pumping conditions, resulting in the need for additional design remedies.
Another level of complexity also arises because the nature of the material deposit from the TiCl.sub.4 /NH.sub.3 reaction is temperature dependent. Therefore, TiN film deposition is often performed at a temperature of preferably above 600.degree. C. In designing a TiN deposition chamber using a high temperature reaction, it is also desirable to maintain the exterior chamber walls at a lower temperature to ensure the safety of operating personnel. Such a high temperature chemical vapor deposition chamber for TiN film deposition is described in a commonly-assigned U.S. patent application Ser. No. 09/211,998, entitled "High Temperature Chemical Vapor Deposition Chamber", filed on Dec. 14, 1998, and is herein incorporated by reference. This high temperature chamber comprises a heated liner which is thermally isolated from the chamber body such that the chamber exterior remains at a temperature of about 60.degree. C. Since TiN film or reaction by-products are also deposited on the interior surfaces of the chamber, periodic chamber cleaning is needed to maintain reliable process performance. It is known in the art that for the TiCl.sub.4 /NH.sub.3 based chemistry, a small amount of TiN film is formed at a temperature between 150.degree. C. to 250.degree. C. This film can readily be removed by a chlorine-based chamber cleaning process. Below 150.degree. C., however, an adduct salt powder deposit is formed, but it is resistant to the chlorine-based cleaning process. It is thus highly desirable to maintain the interior walls of the chamber and exhaust assembly at a temperature between 150.degree. C. to 250.degree. C. to facilitate routine chamber cleaning and system maintenance.
Therefore, a need exists in the art for a temperature controlled exhaust system.